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Tetralogy of Fallot (fah-LO) is a combination of four birth defects that together affect the structure of the heart and how blood flows through it.

Each year, 4 out of every 10,000 babies born in the United States have the condition, which was named after the French doctor who first described it in the late 1800s, Étienne Fallot. About 10% of all babies born with a heart problem have tetralogy of Fallot (TOF).

The four defects that together make up tetralogy of Fallot are:

Ventricular septal defect (VSD), which is a hole in the septum, or wall, separating the two lower chambers, or ventricles, of the heart. The septum acts as a barrier that prevents blood from both sides of the heart from mixing together. But when there is a VSD, blood high in oxygen from the left ventricle can mix with blood low in oxygen from the right ventricle.

Pulmonary stenosis, a narrowing or thickening of the valve that connects the right ventricle to the pulmonary artery, a blood vessel that carries low-oxygen blood from the heart to the lungs, where the blood receives more oxygen and then returns to the heart. With pulmonary stenosis, the heart has to work harder than normal to pump blood to the lungs. Often, the amount of blood reaching the lungs is below normal.

Right ventricular hypertrophy (hi-PER-truh-fee), which is a thickening of the muscular wall of the right ventricle.

An "overriding aorta," which means the artery that carries high-oxygen blood to the body is out of place and arises above both ventricles, instead of just the left ventricle, as in a healthy heart. This allows some blood that is low in oxygen to flow into the aorta and out to the body, instead of to the pulmonary artery, which would normally take it to the lungs to pick up oxygen.

The combined effect of these defects is an inadequate supply of blood to the lungs, which causes blood low in oxygen to circulate to the rest of the body. This lower oxygen level causes cyanosis, which is a blue or purple tint to the skin, lips, and fingernails.

Children with tetralogy of Fallot:

might experience dizziness, fainting, or seizures

are at a higher risk of developing an infection of the inner layer of the heart called endocarditis

can have an irregular heartbeat, called an arrhythmia, which with TOF is caused by elevated pressure in the right side of the heart

A child whose TOF is not repaired might need to limit his or her participation in competitive sports and other physical activities. Many infants who have surgery to correct the defect do very well, participate in normal kid activities, and live to adulthood.

Causes

Science has not yet identified a specific cause for tetralogy of Fallot in all cases, but genetics is believed to play a role. Someone born with TOF seems more likely to have a child with it.

Mothers who contract rubella or other viral illnesses during their pregnancies are at a higher risk of giving birth to babies with TOF. Other risk factors and conditions include poor nutrition, alcohol abuse, diabetes, and mother's age (over 40).

According to the Centers for Disease Control and Prevention (CDC), the presence of certain environmental factors, such as carbon monoxide, might increase a mother's chances of delivering a baby with TOF. In addition, children who have certain genetic disorders, such as Down syndrome and DiGeorge syndrome, often have congenital heart defects, including tetralogy of Fallot.

Signs

One of the most common signs of tetralogy of Fallot is cyanosis (a blue or purple tint to the baby's skin, lips, and fingernails). A child with TOF might experience sudden episodes of cyanosis, called "Tet spells," during crying or feeding.

Other signs include:

heart murmur

fussiness

easy tiring with exertion

difficulty breathing

fatigue

rapid heartbeat (palpitations)

fainting

"clubbing," where the skin or bones around the tips of fingers are widened or rounded

Diagnosis

Your doctor may use several diagnostic tests to determine if your child has tetralogy of Fallot, including:

pulse oximeter: a small sensor that clips onto the fingertip, toe, or ear and measures how much oxygen is in the blood

echocardiogram, or "echo": an ultrasound picture of the heart structures (chambers, walls, and valves). It records the motion of the blood through the heart and can measure the direction and speed of blood flow within the heart structures.

cardiac catheterization: a thin, flexible tube called a catheter is inserted into the heart, usually through a vein in the leg or arm, and provides information about the heart structures as well as blood pressure and blood oxygen levels within the heart chambers. Sometimes a device will be inserted into the heart or blood vessels through the heart catheter.

Treatment

Tetralogy of Fallot is repaired through open-heart surgery soon after birth or later in infancy, depending on the baby's health and weight and severity of defects and symptoms.

The two surgical options are:

Complete intracardiac repair: the surgeon widens or replaces the pulmonary valve and enlarges the passageway between the right ventricle and the pulmonary artery to improve blood flow to the lungs. Then, the ventricular septal defect is patched to stop the mixing of high-oxygen blood with low-oxygen blood between the ventricles.

These repairs also fix the two remaining defects (overriding aorta and right ventricular hypertrophy). Because the right ventricle doesn't have to work as hard to pump blood into the lungs, the thickness of the ventricle wall will decrease. And the patched VSD prevents blood with low oxygen from flowing into the aorta.

Temporary or palliative surgery: only minor repairs are made to improve blood flow to the lungs. This usually only occurs when the baby is too weak or small to undergo full surgery. In the temporary surgery, the surgeon creates a secondary route for blood to travel to the lungs for oxygen. This is done by placing a small tube, called a shunt, between a large artery branching off the aorta and the pulmonary artery.

Later when the baby grows stronger, the full repair is performed.

Most babies born with tetralogy of Fallot do very well and survive to adulthood, but require yearly follow-up with a heart specialist.